Driving mechanism for selectors



Jan. 12, 194.3. J. E. HANSSON 2,307,886

DRIVING MECHANISM FOR SELECTORS Original Filed Oct. 14, 1937 '4Sheets-Sheet l Fig.1 5

PI P2 HANSSON DRIVING ZIIECHANISM FOR SELEGTORS Griginal Filed Got. 14,1957 4 Sheets-Sheet 2 Vmm 1 92/97 J. 4:. amym Jan. 12, 1943. .1. E.HANSSVON 2,307,886

DRIVING MECHANISM FOR SELECTORS Original Filed Oct. 14, 1957 4Sheets-Sheet 3 Fig.6

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J lgpsda'? Jan. 12, 1943. I J, E, HANSSON 2,307,886

DRIVING MECHANISM FOR SELECTORS Original Filed Oct. 14, 1937 4Sheets-Sheet 4 INVENTOR,

ATTORN YS Patented Jan. 12, 1943 DRIVING MECHANISM FOR SELECTORS JohnEdvard Hansson, Stockholm, Sweden, as-

signor to Tclefonaktiebolaget L. M. Ericsson, Stockholm, Sweden, acompany of Sweden 'Continuation of application Serial No. 169,054,

October 14, 1937.

4 Claims.

The present invention relates to a driving mechanism for selectors ofthe type used in remote control systems, particularly in telephonesystems. Such selectors are driven either step by step by means ofimpulse controlled electromagnets or continuously by means of motors,each motor driving either a group of selectors or only an individualselector. Motor operation of selectors as distinguished fromstep-by-step operation is preferable in cases when the wiper velocitiesare high, because through such operation the chocks and resultantstresses in the selector material which occur in the step-wise operationare avoided. However, motor operation entails also certaininconveniences. With the ever increasing requirements which are put onthe velocity of the wipers it has been found diiiicult reliably toeffect testing on the bank contacts of the selectors and to bring theselector to a standstill. In selectors with indi vidual motor drive, onehas also found it difficult to obtain in the necessarily very smallmotors the starting moments required for starting the selector andbraking moments for centering the same.

The present invention has for its objects to eliminate saidinconveniences and consists essentially therein that the selector isprovided with a mechanism known per se for transmitting the movement ofthe motor shaft to the wipers, consisting for example of a pin Wheel anda rack, which mechanism is adapted to transform the substantiallyconstant velocity of the motor shaft to a periodically changing velocityof the wiper. The invention also involves the advantage that the meanvelocity of the wipers can be considerably increased beyond the limitdetermined by such functions of the selector as starting, contacttesting and centering, because all or some of said functions can bebrought to take place during the periods of lower velocity which fallbetween the velocity maxima. According to a preferred embodiment of theinvention the transmission mechanism. is dimensioned in such a mannerwith respect to the distances between the bank contacts that the maximaof the wiper velocity fall between the testing positions of the wipers.

The invention will now be described more in detail having reference tothe drawings accompanying this specification and forming part thereof,in which Figures 1 and 2 show a detail of an embodiment of the inventionin side view and in plan view respectively This application May 4, 1940,Serial No. 333,411.

In Sweden October Figures 3 and 4 are diagrams showing the re lationbetween the space passed over by the selector wipers in Figures 1 and 2and time;

Figure 5 is a corresponding diagram for the velocity as a function ofthe time.

Figure 6 is a corresponding diagram for the acceleration as a functionof the time.

Figure '7 is a diagrammatic perspective view of a telephone switchhaving a motor driven mechanism constructed in accordance with theinvention.

Referring to the drawings in detail, a motor M, Fig. 7, drives a shaft Aprovided at its end surface with pegs or pins Pi and P2 which areparallel with the axis of rotation of the shaft and are in engagementwith teeth Ti, T2 and T3, Figs. 1. and 2 on a rack BK serving as a wiperholder. The axis of rotation of the shaft A is perpendicular to thewiper holder rack BK, so that a turning of the shaft A in the directionindicated by the arrow in Figure 1 will result in a lowering of the pinPl into the space between the teeth TI and T2 and a raising of the pinP2, bringing the latter out of engagement with the teeth T2 and T3. Thewiper holder rack is assumed to be so arranged on the selector, of whichonly a sliding surface S serving as a guide is shown in Fig. 1, thatupon rotation of the shaft A the rack BK will be advancedlongitudinally, the rack then moving between bank contacts. As shown inFigure '7, the bank contacts of the selector consists of parallel barewires extending transversely of the racks, two of which are illustratedand designated as BK! and BK2. The rack BKI carries the line wipers LW,only one of which is visible on the drawings. the other being thenlocated at the opposite side of the rack. The other rack BK2 carries thetesting wiper TW. In testing the selector the motor shaft A will rotatein the direction indcated by the arrows.

The motor is included in a circuit I, having a normally closed contactml and a normally open contact m2. The contact ml is controlled by atest relay TR included in the test circuit 2, which is controlled overthe test wiper TW, the appertaining test wires W2 and contact n whichare open, when the corresponding line is engaged, and closed, when theappertaining line is free.

The selector is started by the motor circuit 1 being closed at thecontact m2. When the test wiper TW finds a disengaged line which, in theexample shown in the drawing, is the last line of the contact bank, thetest circuit is closed through the test relay TR, the test wiper TW, the

contact wire W2 and the appertaining contact 21.. The relay TR uponenergizing opens the motor circuit whereby the racks come to restexactly in the correct contact position, in which position both rods PIand P2 engage the teeth of the racks. The motor may be provided withknown means for stopping the motor shaft at the moment of interruptionof the motor-circuit. In Figure 3 two of said bank contacts are represented by the two hatched circles Wl and consecutive positions of thewiper carried by one of the racks are shown at Bl, B2, B3 and B4. Thedriving pins PI and P2 are represented in Figure 3 by the twouncompleted circles uppermost in the figure. Said figure is alsointended to show that in the embodiment illustrated, the distancebetween the centres of the two adjacent contacts WI is equal to thedistance between the centres of the driving pins. In other words, thepitch of the rack is equal to the pitch of the bank contacts. The sameresult can be obtained, of course, by means of a gearing ha ing someother suitable ratio of transmission. The pin wheel is provided with twodiametrically opposed pins which means, as will be clear from thefollowing, that the periods of maximum velocity of the wipers will occurbetween the testing positions thereof. If the shaft A is rotated at auniform velocity in the direction indicated by the arrow in Figure 1,the pin Pl will perform the above mentioned movement downwards. Providedthat the limiting surfaces of the teeth are parallel with the axis ofthe driving pins and are perpendicular to the direction of movement ofthe rack and that, furthermore, there is a certain play between the pinPI and the teeth Ti and T2, the rack will, to begin with, have no oronly an insignificant movement. For this reason and because of thedirection of application of the force between the pin PI and the toothP2 there will be required only a very small starting moment for puttingthe shaft in motion. According as the angle of rotation of the shaft isincreased the velocity at which the rack BK is displaced is alsoincreased and said velocity will obtain its maximum for an angle ofrotation of the shaft of 90. Thereafter the velocity of the rack will bedecreased until the shaft has been rotated through 180 and the pin P!has taken the place of the pin P2. The above operation is repeated oncontinuing the rotation of the shaft in the same direction.

The above reasoning is illustrated through the diagrams in Figures 3 to6. In Figure 3 the centre of rotation of the shaft A is designated C. Inthe starting position of the selector the wiper contact occupies itsposition BI testing on the left hand'bank contact Wi. The relationbetween the space V passed over by the wiper and the angle of rotationon of the shaft A is readily obtained in the manner shown in the figure.The mathematical expression for the corresponding curve is, if R.designates half the distance between the centres of the pins (see pointM on the curve),

V=R (1cos a) The relation between the space V passed over by the wiperand the time t can be expressed for instance as V=f(t). If R=1 and ifthe angular velocity of the shaft A is constant and equal to w thefollowing will be the relation between V and t:

VII

As will be clear from Figures 3 and 4 the space changes to begin withonly slowly with the time. After the wiper contact has reached itsposition B2 and consequently is out of engagement with the left handbank contact WI the space will increase almost proportionally to thetime, and after the position B3 of the wiper has been reached it willincrease more and more slowly. For comparison a straight line UN hasbeen drawn which represents th relation between space and time for atoothed gearing. After the space between the adjacent contacts has beenpassed over by the wiper contact, the space-time curve for the next halfrevolution of the shaft can be obtained by displacing the coordinatesparallelly with themselves until the origin 0 in Figure 4 coincides withthe point M.

The wiper velocity as a function of the time will be readily obtained byderiving The wiper velocity is thus a sine function of the time (Figure5). The Velocity is zero in the points 0 and L, i. e. at the moments oftesting, and reaches its maximum between said points of time. Byparallel displacement of the coordinates, so that the origin 0 coincideswith the point L, the velocity curve for the next half revolution of theshaft A will be obtained. As will be clear from the velocity curve onewill obtain for each step in a device according to the invention a lowstarting and braking velocity which results in a long testing time forthe wiper. For the same reason the power required by the motor drivingthe shaft A on starting and during the testing of the wiper contact willbe small while at the same time the motor power available is utilized inthe best possible manner between the periods of testing.

The acceleration of the wiper is The acceleration of the shaft A (Figure6) thus changes suddenly from a positive value (acceleration) to anegative value (retardation) (displacement of the origin to the pointQ). Also the curve according to Figure 6 illustrates the properties ofthe driving arrangement previously referred to which make it suitablefor selector operation. The acceleration passes for each period throughzero, namely once continuously, when the velocity reaches its maximumvalue, and once suddenly, when the velocity is zero. On account of theplay between driving pin and tooth surface previously referred to saidlatter zero value of the acceleration will remain for a short timeresulting in that the driving moment which the driving motor is calledupon to produce at the eginning of each period will be small.

A further advantage found in the driving arrangement according to theinvention is that if the shaft is brought to a standstill in theposition of the pin wheel shown in Figure 1 said wheel will lock thebrush rack rendering impossible any transmission of inertia forces fromthe tooth rack to the motor. As will be clear from Figures 1 to 3 saidlocking occurs exactly in the contact positions. In operation withindividual motors, the invention thus involves the advantage that themass to be braked by the motor is small, since the mass of the rack neednot be included therein. Said condition is of special importance whenthe motor is to be braked up and the selector centered through anelectromagnetic braking field.

The invention is, of course, not limited to the embodiment shown but canbe varied in many difierent ways without receding from the idea of theinvention. To obtain the movement defined in the main claim one can thususe a rack with teeth having cycloidal limiting surfaces, thegeneratrices of which are parallel with the axis of the driving pins.One can also use maltese crosses, toothed gearings having cylinderlocking, et cetera.

I claim:

1. In a telephone switch, a number of wipers, a rack cooperating withsaid wipers, a motor for rotation at a substantially constant speed, amovement transmission mechanism comprising a pin wheel for twodiametrically opposed driving pins coacting with said rack to impart tothe wipers a periodically varying speed, and field contacts so arrangedwith respect to said mechanism that the slower phase of the variablespeed of the wipers coincides with the contact making phase of themovement.

2. A telephone switch as claimed in claim 1 in which the centre of thedriving shaft is positioned between the surfaces through the tops andthe roots of the teeth of the rack.

3. A telephone switch as claimed in claim 1 in which the distancebetween the centres of the driving pins is equal to the distance betweenthe centres of the field contacts.

4. In a telephone switch a number of wipers, a rack cooperating withsaid wipers, a motor for rotation at a substantially constant speed, amovement transmission mechanism comprising a pin wheel for twodiametrically opposed driving pins coacting with said rack to impart tothe wipers a periodically varying speed, field contacts so arranged withrespect to said mechanism that the slower phase of the variable speed ofthe wipers coincides with the contact making phase of the movement, andelectrical testing means cooperating with said wipers to stop themovement of the switch in accurate position relatively to the fieldcontacts.

JOHN EDVARD HANSSON.

